1. Field of the invention
The present invention relates to a strong magnetic thrust force type actuator producing a relatively large magnetic thrust for use within an industrial robot, or the like.
2. Description of the Prior Art
Conventional linear pulse motors comprise a primary member and a secondary member. Generally the primary member is an electrically supplied member, in other words, an electromagnetically exciting member. Accordingly, the primary member travels along the secondary member in a linear, reciprocating mode when a pulse current is supplied to the primary member. In this case, the primary member is movable, while the secondary member is stationary, but either the primary or secondary member can be movable.
FIG. 1 shows a conventional linear pulse motor. Numeral 1 designates a secondary member which is an elongate magnetic material plate, the upper side of which includes rectangular teeth 1a and grooves 1b along the longitudinal extent and with an equal pitch thereof. Above the teeth 1a and grooves 1b, primary member 2 is positioned with a predetermined space defined between the primary and secondary members. This primary member 2 is movably supported by means of a supporting member, such as, for example a roller, wheel, or the like. Primary member 2 comprises core 4 for the A-phase and core 5 for the B-phase, the cores respectively comprising magnetic poles 4a and 4b for core 4, and magnetic poles 5a and 5b for core 5; coils 6a and 6b wound around magnetic poles 4a and 4b, respectively; coils 7a and 7b wound around magnetic poles 5a and 5b, respectively; permanent magnets 8 and 9 disposed upon cores 4 and 5, in which the N-pole of permanent magnet 8 faces the upper surface of core 4, while the S-pole of permanent magnet 9 faces the upper surface of core 5, respectively; and a cover plate 10, formed from a magnetic material, for covering permanent magnets 8 and 9. The lower side of magnetic pole 4a has pole teeth 14a and grooves 14c, each of which is formed with an equal pitch. The lower side of magnetic poles 4b, 5a, and 5b each has similar pole teeth 14b, 15a, and 15b, and grooves 14d, 15c, and 15d, respectively.
Assuming that the pitch of rectangular teeth 1a of secondary member 1 is defined by means of the distance P, each of the pole teeth 14b, 15a, and 15b is shifted by means of the distance P/4 with respect to rectangular teeth 1a as shown in FIG. 2, and the lower surface of these pole teeth are positioned at the distance G from the upper surface of teeth 1a.
Accordingly, in turn, supplying the pulse current to coils 6a, 6b, 7a, and 7b generates a magnetic flux respectively. These magnetic flux fields and the magnetic flux fields from permanent magnets 8 and 9, in turn, act upon respective magnetic poles 4a, 4b, 5a, and 5b, allowing primary member 2 to travel along secondary member 1 in the longitudinal direction.
Next, as can be appreciated from FIG. 2, primary member 2 traveling along secondary member 1 is described as being based upon a two phase exciting system when supplying a pulse current to coils 6a and 6b in one group, and coils 7a and 7b in the other group. This pulse current energizes magnetic poles 4a, 4b, 5a, and 5b.
In FIG. 2(a), by supplying the pulse current from terminal 6c to terminal 6d for coils 6a and 6b as shown by means of the arrows, and also, supplying by this pulse current from terminal 7d to terminal 7c for coils 7a and 7b as shown by means of the arrow direction, the magnetic flux generated from coil 6a is added to the magnetic flux generated from permanent magnet 8 at magnetic pole 4a for the A-phase, but these magnetic flux field at magnetic pole 4b for the A-phase counteract each other. In a similar manner, the magnetic flux generated from coil 7a is added to the magnetic flux generated from permanent magnet 9 at magnetic pole 5a for the B-phase, but these magnetic flux fields at magnetic pole 5b for the B-phase counteract each other. Resultant magnetic flux .phi..sub.1 is thus generated in the arrow direction as shown in FIG. 2(a). As a result, the magnetic field acts upon pole teeth 14 a and 15a facing rectangular teeth 1a so as to produce a magnetic thrust.
In FIG. 2(b), by supplying the pulse current to coils 6a and 6b in the same direction as shown in FIG. 2(a), and also, by supplying this pulse current to coils 7a and 7b in the opposite direction with respect to the direction shown in FIG. 2(a), magnetic flux .phi..sub.2 is thus generated in the arrow direction as shown in FIG. 2(b). As a result, the magnetic field acts upon pole teeth 14a and 15b facing rectangular teeth 1a so as to produce the magnetic thrust.
In FIG. 2(c), by supplying the pulse current to coils 6a and 6b in the opposite direction with respect to the direction shown in FIG. 2(b), and by supplying this pulse current to coils 7a and 7b in the same direction as shown in FIG. 2(b), magnetic flux .phi..sub.3 is thus generated in the arrow direction as shown in FIG. 2(c). As a result, the magnetic field acts upon pole teeth 14b and 15b facing rectangular teeth 1aso as to produce the magnetic thrust.
Similarly, in FIG. 2(d), by supplying the pulse current to coils 6a and 6b in the same direction as shown in FIG. 2(c), and by supplying this pulse current to coils 7a and 7b in the opposite direction with respect to the direction shown in FIG. 2(c), magnetic flux .phi..sub.4 is thus generated in the arrow direction as shown in FIG. 2(d). As a result, the magnetic field acts upon pole teeth 14b and 15a facing rectangular teeth 1a so as to produce the magnetic thrust.
Accordingly, the pulse current is, in turn, supplied to respective coils 6a, 6b, 7a, and 7b in the order of such FIG. 2(a), FIG. 2(b), FIG. 2(c), and FIG. 2(d). This allows primary member 2 to travel toward the right direction on the drawings, that is, in the direction extending from magnetic pole 4a to magnetic pole 5b. While the pulse current is, in turn, supplied to the respective coils in the order of such FIG. 2(d), FIG. 2(c), FIG. 2(b), and FIG. 2(a), primary member 2 is conversely caused to travel toward the left direction on the drawing, that is, in the direction extending from magnetic pole 5b to magnetic pole 4a.
Generally, such a linear pulse motor is thus used without a closed-loop control circuit for accurately positioning an object at a certain position, which makes use of a driving device for office automation equipment such as, for example, a printer. However, it is difficult to use such a motor within an industrial robot because of the necessarily large magnetic thrust.
According to the linear pulse motor described in the above, in FIG. 2(a), while generating the magnetic thrust at magnetic poles 4a and 5a, each of the magnetic flux fields is counteracted at magnetic poles 4b and 5b, respectively. A resultant magnetic thrust is therefore not developed at magnetic poles 4b and 5b. Similar magnetic thrust patterns are developed at magnetic poles 4a and 5b in FIG. 2(b), magnetic poles 4b and 5b in FIG. 2(c), and magnetic poles 4b and 5a in FIG. 2(d). As a result, the area of magnetic poles 4a, 4b, 5a and 5b which can generate the resultant magnetic thrust is only 50% of the entire magnetic pole area available. If utilized properly, to area is significant in order to produce additional magnetic thrust.